macro_with_atom.exs

# This works
defmodule Resources do
  defmacro __using__(resource) do
    quote bind_quoted: [resource: resource] do
      def one(resource, id), do: IO.puts "/api/#{resource}/#{id}"
    end
  end
end

defmodule MainApp do
  use Resources, :products
  def test, do: one(:products, 12)
end

MainApp.test

macro_with_tuple.exs

# This gives me:
# ** (CompileError) iex:4: function plural/0 undefined
defmodule Resources do
  defmacro __using__({singular, plural}) do
    quote bind_quoted: [singular: singular, plural: plural] do
      def one(singular, id), do: IO.puts "/api/#{plural}/#{id}"
    end
  end
end

defmodule MainApp do
  use Resources, {:product, :products}
  def test, do: one(:products, 12)
end

MainApp.test

macro_with_tuple_and_no_bind_quoted.exs

# This also works
defmodule Resources do
  defmacro __using__({singular, plural}) do
    quote do
      def one(unquote(singular), id), do: IO.puts "/api/#{unquote(plural)}/#{id}"
    end
  end
end

defmodule MainApp do
  use Resources, {:product, :products}
  def test, do: one(:product, 12)
end

MainApp.test

How about

defmodule Resources do
  defmacro __using__({singular, plural}) do
    quote do
      @singular unquote(singular)
      @plural unquote(plural)
      def one(@singular, id), do: IO.puts "/api/#{@plural}/#{id}"
    end
  end
end
defmodule MainApp do
  use Resources, {:product, :products}
  def test, do: one(:product, 12)
end

MainApp.test

?